Label printers are frequently used together with an inspection device such as for example a weighing scale. This combination is widely used in retail stores, where the customers themselves place their purchases (vegetables, fruits, meat, etc.) on the scale and weigh them. After a number associated with the respective merchandise has been entered, the scale calculates the price for the weighed amount and causes the attached label printer to print the price label.
The field of label printers can be divided into different types according to the kind of label being used. On the one hand, there are labels that are adhesively connected to a carrier foil from which they are separated after the printing and delivered through a label output slot. The customer takes the label from the printer and sticks it on the merchandise to be identified. Labels of this type are necessarily of a uniform size, whereby the area available for printing is predetermined. After the label has been separated from the carrier foil, the latter has to be rolled up again, a function that is performed in most cases in the label printer itself. Labels of this type have the further disadvantage that exchanging or loading a new label roll is complicated and that special measures are necessary to detect the label on the carrier foil and to synchronize the paper-feeding mechanism with the print unit accordingly.
The need to overcome the drawbacks of a carrier foil led to the development of linerless labels, which can be described as label paper that is coated on one side with an adhesive. In contrast to labels on carrier foils, this linerless type of label requires a cutting unit to separate the printed linerless label from the unprinted linerless label paper ribbon. The contact between the blades of the cutting unit and the label paper can leave residual amounts of adhesive remaining on the blades which, over time, can affect the cutting performance. This can lead to unclean cuts, or the cutting unit can even jam up.
According to the present state of the art, two solutions are known to counteract the tendency of the blades getting stuck. One solution is to apply the adhesive coating not as a continuous layer on the label paper, but to leave uncoated gaps which are used to separate the labels at the respective locations. This has the disadvantage that the size of the label is again predetermined, as the label is always cut at the next-following gap of the adhesive. Depending on the interval of adhesive area and uncoated gap, the length of label paper used can be more for one label and less for another, but normally it is always larger than necessary. In addition, it is necessary to establish synchronization between the feed mechanism and the cutting unit, so that the cutting occurs only at the locations of the uncoated gaps. This is accomplished in most cases through markings on the linerless label ribbon. However, the manufacturing cost for the label paper is enormously increased by the process of applying the markings and the adhesive coating with the uncoated gaps.
Also known is a type of label paper that does not carry a full-surface coating of adhesive but where the adhesive is applied in a pattern of coated and uncoated areas. Such patterns can be analogous to a line-hatching, for example narrow stripes running at about 45° across the linerless label ribbon, as well as crossed or V-shaped stripes.
According to another solution presented in EP 1 621 465 A2 or JP 2015 221 487 A1, the blades are moistened with an oil which reduces the tendency of adhesive to stick to the blades. At least one of the blades is immersed in an oil bath or is wiped over an oil-soaked pad whereby the blade is moistened with oil. This has the obvious drawback that oil residues remain on the label after its separation from the ribbon, which is on the one hand detrimental to the adhesive bond between the label and the attachment area (the label can be peeled off more easily), while on the other hand it is deemed unacceptable for the customers to get oil on their fingers.
The object of the embodiments disclosed here is to provide a method which overcomes the drawbacks of the state of the art, specifically a method which allows the label to be separated at any desired place without causing a degradation of cutting performance of the blade or the label printer, and without requiring the blades to be wetted with oil.